The present invention relates to new PCD (polycrystalline diamond) or PcBN (polycrystalline cubic boron nitride) tools with excellent properties in tools for the wood industry. More particularly, the invention relates to PCD or PcBN in which a corrosion and oxidation resistant phase has been distributed in the skeleton of diamonds or cBN-particles characterized by extensive bonding between the hard particles. This corrosion and oxidation resistant phase is based on cobalt and/or nickel chrome.
Reconstituted wood products, such as medium density fiber board and chip board, are, together with solid wood, the main raw materials in the furniture industry. They are also used in the housing industry to some extent.
These products are machined with a variety of tool materials, from high speed steel to cemented carbide to polycrystalline diamond. A leading role is being played by tools made with cemented carbide and PCD or PcBN-tools.
The composition of PCD or PcBN used for woodworking tools consist generally of diamonds or cBN with cobalt as an intergranular phase. Sometimes small amounts of other carbides, nitrides or carbonitrides are added.
The constitution of the PCD are built up by one or several layers/translayers with different compositions regarding diamond contents and cobalt.
Abrasion has been thought to be the primary mechanism of tool wear when machining reconstituted wood products and solid wood. Recent work has proven that chemical mechanisms such as corrosion and oxidation play a significant role in the degradation of cutting edges, as the temperature increases dramatically during the machining process.
The chemical degradation of existing PCD and PcBN-tools is at least a two stage process when machining wood products.
At first, the degradation occurs at a low temperature (300-500.degree. C.), in the early period of cutting. As the tool temperature rises, the wood products decompose and numerous chemicals are introduced in the cutting environment. More than 200 different compounds have been identified upon the destructive distillation of wood. The machining of medium density fiber board and particle board produces even more decomposition products. These products contain also a binder such as urea, formaldehyde, wax and glue fillers and extenders and possibly chemicals added as flame retardants. The decomposition products formed are highly corrosive and attack the cobalt-phase that fills the voids between the hard particles. When this occurs, the diamond-grains loses the sites of the diamond-diamond contact due to the high mechanical stresses and the cutting edge loses its sharpness and its cutting capability.
As the temperature rises above 500.degree. C., the decomposition products are violatised and removed, but degradation of the cutting edge continues by oxidation of the cobalt phase in air. The oxides formed are readily removed by mechanical action, resulting in a fast degradation of the sharpness of the cutting edge.